The present invention relates generally to floating breakwaters, and more particularly, to floating breakwater systems capable of rapid deployment and retrieval, and capable of breaking or attenuating wave action in open water. In this application, xe2x80x9copen waterxe2x80x9d is used to denote any open water including ocean water, lake water, river water, dam water, and the like.
Breakwaters are typically either bottom-mounted or floating. Bottom-mounted structures are generally composed of large rocks (xe2x80x9crip-rapxe2x80x9d) or concrete, and are massive permanent structures. Floating breakwaters have been used for some time as non-permanent structures at harbor entrances, swimming beaches, offshore construction, or for military operations. Typically, these structures include a substantially submerged element which has enough inertial mass to absorb incoming wave energy, and a buoyant element to enable the structure to float. Such floating structures may be moored in a relatively fixed position by lines attached to anchoring points.
Various systems have been developed to achieve a floating breakwater. Some systems have used modular concrete shells or steel frames connected to each other by cables, with inner liners to provide buoyancy. These systems enjoy the advantage of strength and durability, but are massive and cannot easily be launched from, nor retrieved to, a dock or deck of a vessel. Furthermore, because such systems must typically be towed to their destination, they often lack the advantage of rapid deployment.
Thus, despite the use of floating breakwaters for some time, history has witnessed numerous maritime incidents in which ships have run aground in high seas while carrying valuable cargo. In many such incidents, retrieval of such cargo by other vessels has proven difficult or impossible due to an inability to rapidly attenuate wave action in the vicinity of the stricken vessel. Furthermore, certain vessels may need protected anchorage, and a need has been expressed for a robust and rapidly deployable breakwater system that can be deployed in water depths adequate for deep draft vessels, for lightering to smaller vessels or to offload vessels to other vessels or shore during high seas. Further uses for a rapidly deployable floating breakwater include protection of construction sites, swimming beaches, and beach erosion protection during reclamation efforts.
Accordingly, there exists a need for a floating breakwater system which is economical to build, which is capable of being rapidly deployed and retrieved for re-use, and which is capable of attenuating substantial wave action in open water. The present invention addresses these and other needs.
Briefly, and in general terms, the present invention is directed to a new and improved system and apparatus for a transportable and rapidly deployable floating breakwater adapted to attenuate wave action in open water. The floating breakwater includes a pressurized structure made of flexible material, which is especially configured and adapted to have enhanced stiffness and rigidity when deployed, desirable characteristics for effective wave attenuation. When properly positioned and deployed in an area of undesired wave action, the breakwater of the present invention is capable of creating a protected area of attenuated waves in the lee of the breakwater structure.
In a preferred embodiment of the invention, the breakwater includes a primary barrier in the form of an elongate tubular structure of large cross sectional size or diameter with closed ends, adapted, in the deployed state, to contain water or other liquid which is pressurized to a pressure substantially greater than that of the surrounding water. As used herein, xe2x80x9csubstantially greaterxe2x80x9d means a difference in pressure which is adequate to maintain the stiffness and achieve the buckle and wrinkle resistance required for the purpose of wave attenuation. It will be appreciated that such pressurization induces tensile forces in the material forming the wall of the primary barrier, and that such tensile forces enhance the wrinkle and buckle resistance of the material, thus enhancing the overall stiffness of the breakwater, which is a highly desirable characteristic for an effective floating breakwater. Stiffening the breakwater by this means is simple and highly efficient, as it does not require additional structural material which would otherwise be costly and add weight to the breakwater.
In a further aspect of the invention, the breakwater may be adapted so that, after its initial deployment and pressurization, the water within the primary barrier may be continually or periodically re-pressurized throughout the period of deployment of the breakwater in order to maintain a substantially constant level of pressure, or to set the pressure at a different level in order to accommodate a changed sea condition.
A flotation element may be attached to or incorporated into the primary barrier to ensure positive buoyancy of the breakwater at all times. In addition, overtopping barriers may be attached to the top of the primary barrier, adapted to be buoyant in the deployed state and to attenuate wave action which would otherwise overtop the primary barrier.
The breakwater of the present invention is adapted to be expanded from a collapsed condition to an expanded condition in the deployed state. In its deployed condition, the floating breakwater is preferably moored by at least two points along its length and prevented from drifting by mooring lines attached to the ocean bottom or other suitable fixed geographical point. In a deployed state, it is often desirable for the primary barrier to have a relatively large diameter and length. Diameters of between 2 feet and 30 feet may be suitable, depending on prevailing conditions.
In a further aspect, the primary barrier of the invention may be enclosed in or surrounded by a tubular jacket adapted to withstand the forces of the pressurized water within the primary barrier, and to further strengthen and stiffen the primary barrier. In a preferred embodiment, the jacket may be formed of circumferential and longitudinal straps interwoven with each other.
Although a single breakwater unit may be used, a breakwater system may comprise a plurality of breakwater units, incrementally added or subtracted, and arranged to relate to each other in a variety of configurations, depending on prevailing conditions.
The breakwater of the present invention can be used in situations where a permanent breakwater is not feasible, available, or timely. It is also suitable for use in transient conditions, so that it may be temporarily removed if a particularly aggressive sea condition is expected, or if seasonal conditions do not demand the protection of the breakwater. The breakwater of the present invention also has the advantages of being capable of rapid deployment from, and retrieval to, a place of storage on a reel or pallets positioned on a dock or on the deck of a vessel; of being deployed and towed to a desired location, if desired; of being rapidly expanded by filling with water; of having the ability to withstand high seas with little probability of structural failure; of being unlikely to damage vessels with which it may come into contact; and of being lightweight, inexpensive, durable, transportable, and repairable.
These and other objects and advantages of the invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings of illustrative embodiments.